Gunmetal, easily.

So obscure it doesn't even have 70 wishes on the list.

oh shit that looks cool

Oh, at first I thought you meant this Gunmetal (where you can transform between a mech and a jet):
https://youtu.be/W-REbas9K0A

Action Doom 2: Urban Brawl is a cool little freeware title adapted from a Doom total conversion. Nice comic-book graphic style, and an unusual focus on makeshift melee weapons.

Less obscure, but I also really liked Project: Snowblind. It began life as a Deus Ex spin-off, only to lose the license during development, but the influence of that world really shows. The game is pretty much a stock "cinematic FPS", though your character gets periodic upgrades in the form of special powers, and it's also at least slightly less linear than a lot of other games of that style. Very short (to the point where I was surprised and confused that the game had just ended), but a pretty fun ride nonetheless.

No kidding.

Glad I'm not the only one who's heard of In Pursuit of Greed. It could be a bit frustrating to navigate but I loved the soundtrack.
https://www.youtube.com/watch?v=dXgEM42PbGc

Believe the same guy who worked on the Crusader No Regret/Remorse soundtrack worked on it.

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Yes!
But this way they can do "20 Years Later..." in the next game and everybody laughs because it's true.

Never played obscure shooters, except Rex Blade and Island Peril. But I played them too little to like or dislike them.

Brilliant!

The first Skynet by Bethsheda.

I guess No One Lives Forever isn't obscure on GOG, but it's still not exactly well known in general.

Other than that, a fairly recent one- Angels Fall First is basically indie Battlefront II. Asymetric objective-based maps with ground and space combat, and full AI support that keeps being tweaked to make player-and-bot matches more fun than they usually are when you're playing 128-player games alone.

Cybermage. Never played it, but used to drool over its promotional images in some of my gaming magazines.

Another vote for the first No One Lives Forever. I still don't know if that reloaded version is legal or not.

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Black on PS2/Xbox was a fun game. Developed by Criterion from 2004-2005, it's a good-looking game for it's time. There's nothing super special about it but it was a fun shooter with a budget action-movie-level story that was basically just an excuse to walk through levels and shoot some dudes, although the game is notable for punishing attempts to go all-out Rambo, as taking cover is rather necessary at most times and health doesn't regenerate. It's a fun little buried treasure that you can probably still download on Xbox 360, I think? There was also a spiritual-successor developed called Bodycount that received much less praise than the original and the series as a whole has more or less faded into obscurity.